Evaluation of Sustainability-Oriented Route to Produce CoCrFeNi High-Entropy Alloy Spherical Agglomerates Using Hydrogen Reduction

초록

This paper presents a potentially lower-carbon high-entropy alloy (HEA) powder fabrication route that uses metal oxide powders as raw feedstock and employs hydrogen reduction to produce only water vapor as a byproduct. Conventional fabrication routes for HEA powders such as casting, gas atomization, and mechanical alloying rely on metallic raw materials whose production generates considerable CO2 emissions during melting, atomization, and powder synthesis. These carbon-intensive processes highlight the need for alternative sustainable feedstocks. Chromium, which is a corrosion-resistant and oxidation-stable material to be suitable for extreme environments such as high temperatures and chemically aggressive conditions, was incorporated into HEA. However, the hydrogen reduction of Cr2O3 typically requires high temperatures, which is a major challenge to oxide-based HEA fabrication. This study lowers the processing temperature by forming a solid solution of oxide powders through high-energy milling, promoting oxide solid-solution formation. Milling refines the oxide powders to the nanoscale, improving compositional homogeneity and reducing the activation energy required for Cr2O3 reduction, thereby enabling partial hydrogen reduction at a significantly lower temperature of 1,000 °C. The milled powders were spray dried into spherical agglomerates and hydrogen-reduced, which achieves a sphericity of 0.974. After sintering, the hydrogen-reduced sample exhibited higher hardness (3.23 ± 0.28 GPa) and more uniform distribution than that of the gas-atomized counterpart (1.94 ± 0.40 GPa). The sample sintered from the hydrogen-reduced powder exhibited a more uniform hardness distribution than that of the sample sintered from the gas-atomized powder with lower porosity. © The Author(s), under exclusive licence to Korean Society for Precision Engineering 2026.

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